The cellular architecture of these systems implies location procedures for applying data about the current position of the mobile stations which are connected to the system to a central element so that this system can efficiently lead the communications to the destination stations. For this purpose, the central element manages a list of mobile stations called "system-connectable" so as to identify the stations capable of receiving communications.
As these location procedures generate a considerable amount of traffic on the radio channels, it is necessary to initiate them the least possible so as not to saturate the system.
Recommendation ETS 300 557 of ETSI (European Telecommunications Standards Institute) for the GSM standard states criterions for optimizing the management of these location procedures.
According to this Recommendation, when a location attempt fails due to the fact that the radio coverage is too weak to establish a connection (a case of RANDOM_ACCESS_FAILED), the mobile station is placed in a state called IDLE_NOT_UPDATED in which it is considered unconnectable by the system. Indeed, at the instant at which the location attempt has failed, the mobile station was in an area where the radio coverage was insufficient for the mobile station to establish a radio connection of good quality for receiving communications. The IDLE_NOT_UPDATED state is then assigned thereto to avoid a saturation of the system by the transmission of communications which have a very slim chance of reaching the destination.
The mobile station thus remains in the IDLE_NOT_UPDATED state until one of the following three events happens:
The role of the periodic timer is to confirm to the system every T3212.times.6 minutes via a periodic location the presence of the mobile station in the same geographical area. If the station changes its geographical area, a normal type of location is initiated. In case of a failure of a periodic location, the system considers the mobile turned off or unconnectable and removes the station from the list of connectable stations until a location is carried out successfully.
Thus, according to said Recommendation the periodic timer may expire between 6 minutes and 24 hours after being switched on depending on the coverage area. This implies that in highly unfavorable cases the base station is located in an area of poor coverage with shadowy areas and that neither of the other two events occurs before the periodic timer expires, the mobile station may continue to be unconnectable for several hours, which may be highly detrimental.
However, during this period of time, the mobile station may have been in a position to move without changing cell so as to benefit from a sufficient coverage for the transmission of a communication. But, since no location procedure has been initiated, according to the cited Recommendation the mobile station is still in the IDLE_NOT_UPDATED state, the system does not know the current position of the mobile station and is thus incapable of transmitting a communication to the mobile station.